The present invention relates to improving hiding efficiency in pigmented paints using an itaconic acid functionalized latex binder in combination with a solution of a polymer containing sulfonic acid groups or salts thereof. The efficacy of the TiO2 as a hiding pigment is reduced when TiO2 particles are allowed to come too close together on film formation and drying. It is known that the spacing of TiO2 and its concomitant hiding efficiency can be improved with the aid of emulsion polymers particles adsorbed to the TiO2 particle surface, as disclosed in US 2003/0018103. One of the problems observed with current adsorbing latex technology, particularly latexes prepared using highly reactive functional monomers such as phosphoethylmethacrylate (PEM), is formation of grit arising from the uncontrolled reaction of the reactive adsorbing latex with TiO2. To control grit, the formulator must carefully mix the adsorbing latex with the pigment under controlled conditions to avoid flocculation, which often requires expensive high shear mixing.
Alternatively, grit can be controlled using less reactive adsorbing latexes, for example, latexes prepared from less reactive functional monomers such as itaconic acid (IA). These less reactive functional monomers may also provide a lower cost alternative and improvements in film properties, such as water sensitivity or scrub resistance. Coatings formulations made from these latexes, however, exhibit significantly less hiding than coatings made from the more reactive latexes. U.S. Pat. No. 8,546,467 discloses a process of manipulating the pH within an adsorbing latex prepared with a less reactive monomer (IA) to give reduced grit and better hiding within a paint formulation. This process, while representing an advance in hiding technology, introduces an additional step to the formulator that may lead to a drop in volume solids and an increase in dissolved salts upon neutralizing back to a typical paint pH; such additional steps tend to adversely affect the cost and performance of formulated paints. It would therefore be desirable to discover a simpler way to improve the hiding efficiency of coatings formulated with itaconic acid functionalized binders.